This invention relates to a device, specially intended for household application but also adapted for professional use at public spots, for heating and emulsifying milk and air, which may be variously used and in particular used to prepare such a hot drink as the so-called "cappuccino", which is a mixture of coffee infusate and milk particularly emulsified with air particles. Heat is applied by the injection of steam, whereupon milk is also emulsified. For this purpose, it is necessary that, by the suction effect of the steam from the nozzle, air be drawn in for introduction through the liquid phase milk along with the steam, which air stays in gaseous emulsion with the milk, whereas the steam heats the milk and is either condensed therein or dispersed.
The operator is currently required to find out optimum location of the steam nozzle and the level of the liquid phase milk in order to bring about an appropriate inflow of air and break it up, and to achieve proper metering of the air to be emulsified with the milk. It is frequently expedient to perform a cyclic relative movement of the milk container up and down with respect to the steam nozzle, so as to achieve a desired emulsifying effect; the operation requires skilful handling to prevent objectionable, and occasionally hazardous, splashes of milk and steam leakouts.
Where operations of this kind are to be performed in a house environment, using small household appliances for "espresso" coffee making, the problem is made more complicated by the operator possessing no special experience on the matter, and because in the house very small unit amounts of milk, and hence, small-size containers are apt to be used, which increases the risk of splashing out.